1. Field of the Invention
The present invention relates to a developing device for effecting development with use of a two-component developer containing toner and magnetic carrier, an image forming apparatus, and a cleaning method for the developing device.
2. Description of the Related Art
To date an electrophotographic image forming apparatus has generally been applied to image forming apparatuses such as copying machines and printers. Where the workings of the electrophotographic image forming apparatus are concerned, an electrostatic latent image is formed on a surface of a photoreceptor toner image bearing member). Then, with a toner supplied from a developing device, the electrostatic latent image is developed into a toner image, and the resultant toner image is transferred and fixed onto a recording medium such as a paper sheet. In this way, an image is formed on the recording medium.
In order to achieve formation of images in color and high-quality images as well, recent-model image forming apparatuses employ, as a developing agent, a two-component developer which excels in toner charging stability. The two-component developer is composed of toner and carrier. The toner and the carrier are stirred within a developer tank provided in a developing device of such an image forming apparatus thereby to produce friction between them. Under the friction, the toner can be electrically charged properly.
In recent years, there has been an increasing demand for speedup and miniaturization in image forming apparatuses. For enhanced speed, the two-component developer needs to be electrically charged swiftly and thoroughly while being conveyed quickly. It is particularly necessary for the toner supplied to the developer tank to be dispersed in the two-component developer quickly so as to be electrically charged properly.
In Japanese Unexamined Patent Publication JP-A 10-63081 (1998), there is disclosed a circulation-type developing device composed of two developer conveyance passages through which a two-component developer is passed in circulation and two developer conveying members for conveying the two-component developer with stirring in the developer conveyance passages. In the developing device disclosed in JP-A 10-63081, the two-component developer is conveyed efficiently by the developer conveying member designed in a spiral form.
However, even in the developing device having the spiral developer conveying member that offers high developer conveyance capability, due to centrifugal force and heat resulting from high-speed rotation of the developer conveying member, the developer inconveniently adheres in an aggregated state to the inner wall of the developer tank with the consequence that the flow of the developer is impaired.